Selective hydrogenation process



United States Patent SELECTIVE HYDROGENATION PROCESS Peter K. Baumgarten, Edward J. Hotfmann, and Edward F. Wadley, Baytown, Tex., assignors, by mesne assignments, to Standard Oil Development Company, Elizabeth, N. J., a corporation of Delaware Application September 1, 1950, Serial No. 182,648

2 Claims. (Cl. 196-36) The present invention is directed to a selective hydrogenation process. More particularly, the invention is directed to the hydrogenation of naphthas containing olefins and di-olefins, such as cracked naphthas, under conditions such that the di-olefins are selectively hydrogenated.

The present invention will be described as a hydrogenation process in which a naphtha, such as a cracked naphtha, containing monoand di-olefins is hydrogenated to improve the quality thereof for use as a motor fuel. The steps in the hydrogenation process of the present invention involve contacting the naphtha with a sulfur insensitive catalyst at a temperature in the range between 350 and 650 F. and at a pressure in the range between 15 and 500 pounds per square inch gauge and at a liquid space velocity in the range between 1 and 20 v./v./hour in the presence of a suflicient amount of a hydrogen-containing gas containing at least 10% hydrogen to maintain a molal ratio of gas to naphtha of 1:1 for a fixed set of conditions within the ranges of temperatures, pressures, and space velocities given to obtain maximum conversion of conjugated di-olefins and to form a product suitable for use as a motor fuel. Finally, the product is recovered from contact with the catalyst and may be treated subsequently prior to use as a motor fuel.

The sulfur insensitive catalyst employed in the practice of the present invention may be a sulfide of a heavy metal, such as nickel, molybdenum and tungsten. Mixtures of these catalysts may be employed, such as mixtures of nickel sulfide and tungsten sulfide. The catalyst may be used as such or may be deposited on a suitable carrier material, such as a porous adsorbent inert material, such as clay, kieselguhr, alumina and the like.

The hydrogen-containing gas involved in the practice of the present invention should contain at least 10% of hydrogen and may contain up to 100% of hydrogen. As a preferred range the hydrogen-containing gas will contain from 50 to 100% of hydrogen. The other material present in the gas should be inert from the standpoint of reacting with the cracked naphtha being hydrogenated or deleteriously affecting the catalyst activity. Such inert material may be C1 to C5 parafiinic hydrocarbons, flue gas and the like.

While the space velocity employed in the practice of the present invention may range from 1 to 20 v./v./hour, a preferred range is from 3 to 8 v./ v./hour.

As stated, temperatures may range from 350 to 650 F. with temperatures preferably in the range from 500 to 600 F. Pressures ordinarily may range from 15 to 500 pounds per square inch gauge with a preferred range from 50 to 100 pounds per square inch gauge.

The hydrogenated naphtha or product produced under the foregoing conditions is removed from contact with the catalyst and may be subsequently treated prior to use as a motor fuel. Such treatments may include distillation to recover a desired fraction and/or washing the hydrogenated product with a solution of a caustic alkali such as an aqueous or alcoholic solution of sodium hydroxide having a gravity in the range between 5 and 30 B. to remove hydrogen sulfide and other caustic soluble sulfur compounds which may be present in the feed or result from the hydrogenation reaction. The hydrogenated product may be treated with the alkaline solution prior or subsequent to the distillation step to recover motor fuel constituents.

The present invention is based on the discovery that for any given set of conditions of temperatures, pressures and space velocities in the ranges set out above when employing a hydrogen-containing gas containing at least 10% hydrogen that it is possible to obtain maximum conversion of conjugated di-olefins with a low conversion of mono-olefins if a ratio of gas to naphtha being hydrogenated of 1:1 is maintained. This ratio of 1:1 is independent of the concentration of hydrogen in the gas employed in the hydrogen medium and it is the only ratio that will permit maximum conversion of conjugated diolefins when operating under any fixed set of conditions within the ranges given; for example, for a given set of conditions of temperature, pressure and space velocity by maintaining a ratio of hydrogen-containing gas to naphtha of 1:1 only is it possible to obtain maximum conversion of conjugated di-olefins. Increasing the gas to oil ratio increases mono-olefin conversion with a decrease in conjugated di-olefin content.

The reason that it is important to remove the maximum amount of conjugated di-olefins under a given set of conditions while minimizing the removal of monoolefins is that the di-olefins are recognized to be primary contributors to the formation of gums and engine deposits on use of cracked naphthas in motor fuels. While removal of the conjugated di-olefins may be achieved by subjecting cracked naphtha to catalytic hydrogenation at elevated temperatures in accordance with the prior art teachings such treatments also result in removal of monoolefins by conversion to parafiins. When straight chain mono-olefins are converted to normal paraffins, the octane numbers of the cracked naphtha are seriously impaired. The present invention eliminates the objectionable features of the prior art processes in that the diolefins are selectively hydrogenated while the mono-olefins remain substantially unconverted. The present invention also results in substantial removal of sulfur by conversion of same to sulfur compounds which are easily removed from the product. The present invention is, therefore, based on a discovery that the maximum removal of conjugated di-olefins occurs at a 1:1 gas to oil ratio, other conditions being constant.

The present invention will be further illustrated by the following series of runs in which a naphtha from a thermal cracking operation was contacted with a nickel sulfide-tungsten sulfide catalyst at a temperature of 500 F. and at a pressure of 100 pounds per square inch gauge employing gas from a commercial hydroforming unit containing approximately 72% hydrogen. The naphtha was charged to contact with the catalyst at a space velocity of 6 v./v./hour. The results of these runs are shown in the following table:

Table I Olefin Conversion, 0. F. of H2 Percent Mols Gas per M01 Naphtha 1pIer ap t Conju- Total gated Diane From the foregoing results in Table I, it will be seen that at a ratio of 1 mole of gas per mole of naphtha that 88% of the conjugated diene-olefin content is converted while at the same ratio only 17% of the total olefin content is removed indicating that the di-olefins were selectively hydrogenated. It will be noted that it is only at a ratio of 1:1 that a maximum conversion of di-olefins takes place while minimizing conversion of mono-olefins.

Similar values may be obtained when contacting a cracked naphtha from a thermal cracking unit under conditions such as those represented in the foregoing example. Exemplary of the results obtainable at lower and higher space velocities are the data presented in Table II in which comparisons are made between space velocities of 3 and 12 v./v./hour under similar conditions to those of the preceding example:

Table II 3 V./V./Hr. Con- 12 V./V./Hr. Con- 1 Conjugated.

The data presented in Table II show the same unexpected results as the data presented in Table 1, namely, that at a ratio of 1:1 mole of hydrogen-containing gas per mole of naphtha, maximum conversion of di-olefins takes place with a low conversion of mono-olefins showing that the mono-olefins are substantially unaffected at this ratio.

The data presented in Tables I and II are also presented graphically in the single figure which is a plot of conversion against the mole of gas per mole of naphtha. From an examination of this figure it will be seen that at a ratio of 1:1 maximum conversion of di-olefins is obtained irrespective of the space velocity of the feed in contact with the catalyst while at the ratio of 1:1 the conversion of mono-olefins has not reached a maximum. It will be further noted from an examination of the curves that when a ratio in excess of 1:1 is employed the conversion of di-olefins drops off while the conversion of mono-olefins increases. It may be concluded, therefore, from these results that only at a ratio of 1:1 are the beneficial results of the present invention obtained.

It will be noted that it is the ratio of hydrogen-containing gas to naphtha which is important and not the content of hydrogen contained in the hydrogen containing gas provided the amount of hydrogen contained therein is above Referring again to the data in Tables I and II it will be clear that at a ratio of 1:1 the amount of hydrogen in cubic feet per barrel of naphtha is less than that employed at higher ratios of gas to naphtha. Thus it is important in the practice of the present invention that the ratio of hydrogen-containing gas to naphtha be maintained at 1:1 for a given set of operating conditions.

To illustrate the effect of hydrogen purity additional runs were made in which a naphtha from a thermal cracking operation was contacted with a nickel sulfidetungsten sulfide catalyst at a temperature of 500 F. and at a pressure of 100 pounds per square inch gauge, employing a gas containing 99.7% hydrogen and about 0.3% nitrogen. This gas was carefully purified to exclude oxygen. The aforesaid naphtha was contacted with the catalyst at a space velocity of 6 v./v./hour. The results of these runs are shown in Table III:

Table III Olefin Conversion, 0. F. ofHz/ Percent Mols gas/M01 Naphtha bbkfllfaph- Comugated Total Diem It will be seen from the results of the runs presented in Table III that a ratio of 1.02 mols of gas per mol of naphtha 93% of the conjugated diene olefin were converted with 24% conversion of the total olefins. At a ratio of 2.4 mols of gas per mol of naphtha the total olefin conversion was increased while the conjugated diene olefin conversion decreased slightly. It will be noted that the amount of hydrogen in the second run was over double the amount of that employed in the first run.

While the present invention has been described and illustrated by reference to a naphtha from a thermal cracking operation, it will be apparent to the skilled workman that the invention is not restricted to thermally cracked naphthas. The invention will apply equally to naphthas from catalytic cracking operations and reformed naphthas. As a general statement, the invention may be preferably applied to stocks boiling in the gasoline and naphtha boiling range but may be applied to fractions having a boiling point up to 700 F.

The nature and objects of the present invention having been completely described and illustrated, what we desire to claim as new and useful and to secure by Letters Patent is:

1. A method for hydrogenating a cracked naphtha containing monoand di-olefins to improve the quality thereof for use as a motor fuel which comprises contacting said cracked naphtha with a nickel-tungsten sulfide catalyst at a temperature in the range between 500 and 600 F. at a pressure in the range between 15 and 500 pounds per square inch gauge and at a liquid space velocity in the range between 3 and 12 v./v./hour in the presence of a suflicient amount of a hydrogen-containing gas containing at least 10 mol hydrogen to maintain a mol ratio of gas to cracked naphtha of 1:1 for a fixed set of conditions within the ranges of temperatures, pressures and space velocities given to obtain maximum selective conversion of conjugated di-olefins at low mono-olefin conversion and to form a product suitable for use as a motor fuel and recovering said product.

2. A method for hydrogenating a cracked naphtha containing monoand di-olcfins to improve the quality thereof for use as a motor fuel which comprises contacting said cracked naphtha with a nickel-tungsten sulfide catalyst at a temperature in the range between 500 and 600 F. at a pressure in the range between 60 and 300 pounds per square inch gauge and at a liquid space velocity in the range between 3 and 8 v./v./hour in the presence of a sufiicient amount of a hydrogen-containing gas containing at least 10 mol hydrogen to maintain a mol ratio of gas to cracked naphtha of 1:1 for a fixed set of conditions within the ranges of temperatures, pressures and space velocities given to obtain maxnnum conversion of conjugated diolefins and to form a product suitable for use as a motor fuel and recovering said product.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,002,902 Martin et a1. May 28, 1935 2,392,579 Cole Jan. 8, 1946 2,413,312 Cole Dec. 31, 1946 2,542,970 Jones Feb. 27, 1951 2,623,007 Myers Dec. 23, 1952 

1. A METHOD FOR HYDROGENATING A CRACKED NAPHTHA CONTAINING MONO- AND DI-OLEFINS TO IMPROVE THE QUALITY THEREOF FOR USE AS A MOTOR FUEL WHICH COMPRISES CONTACTING SAID CRACKED NAPHTHA WITH A NICKEL-TUNGSTEN SULFIDE CATALYST AT A TEMPERATURE IN THE RANGE BETWEEN 500* AND 600* F. AT A PRESSURE IN THE RANGE BETWEEN 15 AND 500 POUNDS PER SQUARE INCH GAUGE AND AT A LIQUID SPACE VELOCITY IN THE RANGE BETWEEN 3 AND 12 V./V./HOUR IN THE PRESENCE OF A SUFFICIENT AMOUNT OF A HYDROGEN-CONTAINING 